Field of the Invention
The present invention relates to a halogen-free epoxy resin composition, in particular relates to a halogen-free epoxy resin composition having low dielectric loss characteristics.
Description of Prior Art
As electronic products data processing speed develops rapidly and offer functions diversified, the application frequency increases. 3-6 GHZ will become mainstream. In addition to the higher requirements of the heat resistance of laminate materials, the requirements of the dielectric constant and the dielectric loss value of the laminate materials will be lower and lower.
Existing conventional epoxy glass fiber cloth laminate (FR-4) has difficulty to meet the needs of high-frequency and high-speed development of electronic products, and at the same time substrate materials no longer support traditional mechanical means, and instead integrates with electronic components to form PCBs which becomes a critical means applied by end product manufacturer designers in order to increase product performance. Low signal transfer rate has been a concern when the dielectric constant (Dk) is high, and parts of the signal are converted into heat loss in the substrate materials when the dielectric loss value (Df) is high, reducing DK/Df has become the industry's desired features in substrate materials. Dicyandiamide has been used as a curing agent among the conventional raw materials to produce FR-4. Dicyandiamide has a tertiary amine structure, which can be highly reactive. However, the carbon-nitrogen bond of dicyandiamide is weak, and easily cracks under high temperature. Accordingly, the heat decomposition temperature of the curing agent is low and fails to meet the thermal requirements of lead-free processes. Therefore, along with a wide range of lead-free process implementation in recent years, novolac resins are used more often as curing agents for epoxy resins. The novolac resins have benzene ring structures with high thermal and high-density characteristics, although the cured epoxy structure has superior heat resistance, the dielectric properties of the cured product kept deteriorate.
In the prior arts, active ester curing agents having benzene, naphthalene or biphenyl structure are synthesized as the epoxy resin curing agent, such as IAAN, IABN, TriABN and TAAN. Compare to using conventional novolac compounds, the dielectric constants and dielectric loss values of the cured products obtained are significantly lowered.
Although the above mentioned prior arts using active esters as an epoxy resin cured agent can effectively improve moisture resistance, reduce water absorption, dielectric constant and the dielectric loss values of a cured product, the problem to keep the balance between heat resistance and dielectric properties of the cured product remain unresolved, wherein the balance ensures the cured product having a high glass transition temperature and a low dielectric loss value, and also keeps the dielectric properties in a relatively stable state as frequency changes, as well as keeps the water absorption low.